JP3136864B2 - Electric power steering device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus, and more particularly to an electric power steering apparatus for a vehicle such as an automobile.

[0002]

2. Description of the Related Art Conventionally, an electric power steering apparatus for a vehicle such as an automobile generally has a motor for driving a steering linkage member such as a rack bar via a clutch and a steering gear box, and a control apparatus for controlling the rotation of the motor. The control device is configured to generate a required steering assist force by controlling the motor based on the detection results of various sensors.

As such an electric power steering device, there is, for example, a device described in Japanese Patent Application Laid-Open No. 60-67264. This device is configured to decrease the output torque of a motor that generates an auxiliary steering force as the vehicle speed increases, and increase the output torque of the motor as the steering torque of the driver increases.

[0004]

In the conventional apparatus, a motor target torque is determined by using a motor output torque determined by a steering torque as shown by a solid line in FIG. 6 and a vehicle speed coefficient determined by a vehicle speed as shown in FIG. It is determined by the equation (1).

[0005] In the motor target torque = motor output torque × speed factor (1) wherein the motor output torque is steering torque as shown in solid line in FIG. 6 is saturated by rating exceeds T _MAX motor.

Therefore, the motor target torque when the vehicle speed is 0 km / h is represented by a solid line in FIG.
/ motor target torque when h is represented by a dashed line, also saturated with the steering torque exceeds T _MAX this case, it does not increase further.

[0007] Therefore, when performing hard traveling performing steering of large steering angle the mountain road or the like at a high speed, because the target motor torque steering torque is reduced by the vehicle speed coefficient exceeds T _MAX is saturated As shown in FIG. 8, the steering torque suddenly increases, giving the driver a sense of incongruity and causing poor driveability.

[0008] The present invention has been made in view of the above points,
Steering during high-speed steering operation with a large steering angle by correcting the reduction ratio of the auxiliary steering force according to the increase of the vehicle speed when the steering torque is equal to or greater than the value corresponding to the saturation point of the motor output torque. An object of the present invention is to provide an electric power steering device that prevents a sudden change in torque and improves drivability.

[0009]

FIG. 1 shows the principle of the present invention.

In FIG. 1, a calculating means M1 calculates an auxiliary steering force based on a steering torque.

The first correction means M2 has a value smaller than 1 which decreases as the vehicle speed increases as the vehicle speed increases .
The auxiliary steering force is multiplied by a correction coefficient to reduce and correct the auxiliary steering force.

The control means M3 controls the driving of the electric motor M5 based on the corrected auxiliary steering force, and performs the auxiliary steering by the electric motor M5.

When the steering torque is equal to or greater than the value corresponding to the saturation point of the output torque characteristic of the electric motor, the second correction means M4 decreases the rate of the decrease correction based on the vehicle speed of the first correction means M2. I do.

[0014]

According to the present invention, the rate of reduction of the auxiliary steering force according to the increase of the vehicle speed is reduced and corrected when the steering torque is equal to or greater than the value corresponding to the saturation point of the motor output torque. At the time of operating the steering wheel of the corner, the ratio of the decrease correction of the auxiliary steering force by the first correction means M2 is reduced, the auxiliary steering force becomes larger than before, and a sudden change in the steering torque is prevented.

[0015]

FIG. 2 is a schematic diagram showing one embodiment of an electric power steering apparatus according to the present invention, and FIG. 3 is a block diagram showing an electronic control unit shown in FIG.

In FIG. 2, reference numeral 10 denotes a steering wheel. The steering wheel 10 drives a rack bar 16 via a steering shaft 12 and a steering gear box 14. A power unit 20 is drivingly connected to the steering shaft 12 by a gear reduction mechanism 18. Power unit 20
Has a motor 22, and an electromagnetic clutch 24 for selectively drivingly connecting the gear reduction mechanism 18 and the motor 22.

The steering shaft 12 is provided with a steering angle sensor 26 for detecting a steering angle θ and a torque sensor 28 for detecting a steering torque T. The outputs of these sensors are supplied to an electronic control unit 32. Has become. A signal indicating the vehicle speed V detected by the vehicle speed sensor 34 is also input to the electronic control unit 32.

The electronic control unit 32 includes a microcomputer 38 as shown in FIG.
Reference numeral 8 denotes a central processing unit (CPU) 40, a read only memory (ROM) 42, and a random access memory (R
AM) 44, an input port device 46, and an output port device 48, which are connected to each other by a bidirectional common bus 50.

The input port device 46 has a steering angle sensor 26
Indicating the steering angle θ detected by the torque sensor 2
8 and a signal indicating the vehicle speed V detected by the vehicle speed sensor 34 are input. The input port device 46 appropriately processes the signal input thereto, and in accordance with the instruction of the CPU 40 based on the control program stored in the ROM 42, the CPU and the RAM 4
4 to output the processed signal.

The ROM 42 stores a control program and a map. The CPU 40 performs various calculations and signal processing based on the control program as described later. The output port device 48 outputs a control signal to the motor 22 via the drive circuit 52 according to the instruction of the CPU 40, outputs a control signal to the electromagnetic clutch 24 via the drive circuit 54, and further determines that the motor is locked. Warning lamp 56
Lights up.

FIG. 4 shows a flowchart of one embodiment of the steering control processing executed by the electronic control unit 32.

The operation is started by closing an ignition switch (not shown in FIG. 2). In the flowchart, N indicates the number of times that the motor is locked.

First, in step S10, the clutch is connected by supplying a control signal to the electromagnetic clutch 24 via the drive circuit 54. In step S20, the steering angle sensor 2 is turned on.
A signal indicating the steering angle θ detected by the control unit 6, a signal indicating the steering torque T detected by the torque sensor 28, and a signal indicating the vehicle speed V detected by the vehicle speed sensor 34 are read.

In step S30, the basic assist amount Tab is calculated from the map corresponding to the solid line in FIG. 6 based on the steering torque T read in step S20, and the vehicle speed V read in step S20 is calculated in step S40. The vehicle speed coefficient Kv is calculated from the map corresponding to the solid line in FIG.

The vehicle speed coefficient Kv determined in step S40 in step S60, it is determined whether or less than the maximum value Kv _max, in the case of Kv ≧ Kv _max proceeds to step S100,
If Kv <Kv _max , the process proceeds to step S70. In step S70, the absolute value of the steering torque T detected by the torque sensor 28 becomes the saturation value T _{MAX of the} steering torque shown in FIG.
Determines whether or, | T | <For T _MAX proceeds to step S100, | T | For ≧ T _MAX step S8
Go to 0.

In step S80, a correction coefficient Kriv of the vehicle speed coefficient Kv is calculated by the following equation.

Kriv = α × | T−T _MAX | × β where the coefficient α is a constant, and the coefficient β is a value corresponding to the vehicle speed calculated from the map shown by the broken line in FIG.

[0028] That is, the correction coefficient Kriv is an integer of 1 or more large next higher steering torque T is greater than T _MAX, and the vehicle speed which becomes larger the more large.

Next, in step S90, the vehicle speed coefficient Kv is corrected by multiplying the vehicle speed coefficient Kv by the correction coefficient Kriv.
Go to 100.

In step S100, the basic assist amount Tab determined in step S30 is compared with step S40 or S40.
The assist amount Ta, which is the motor target torque, is calculated by multiplying by the vehicle speed coefficient Kv obtained at 90. Thereafter, in step S110, a control signal corresponding to the assist amount Ta is supplied to the motor 22 via the drive circuit 52,
After the steering assist force is controlled to a value corresponding to the assist amount Ta, the process returns to step S20.

As described above, the steering torque is equal to the motor output torque.
At the saturation point, ie, at the steering torque, _MAXCar
The rate of decrease of the speed coefficient Kv is determined by steps S80 and S90.
It is corrected to decrease. Therefore, the vehicle speed coefficient Kv
Motor output torque, which has been reduced by
The steering force increases, so high-speed steering with a large steering angle on mountain roads
Steering torque even when performing hard driving by performing operations
Does not have a sharp increase like a broken line as shown in FIG.
The characteristics become more stable and drivability is improved.

[0032]

As described above, according to the electric power steering apparatus of the present invention, the ratio of the reduction of the auxiliary steering force according to the increase of the vehicle speed is determined by the value of the steering torque corresponding to the saturation point of the motor output torque. In the above case, the decrease correction ratio of the auxiliary steering force is reduced, the auxiliary steering force becomes larger than before, and a sudden change in the steering torque at the time of operating the steering wheel at a high speed and a large steering angle is prevented. Is very useful in practical use.

[Brief description of the drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a schematic configuration diagram of the device of the present invention.

FIG. 3 is a block diagram of an electronic control device.

FIG. 4 is a flowchart of a steering control process of the device of the present invention.

FIG. 5 is a diagram illustrating a relationship between a steering angle and a steering torque according to the present invention.

FIG. 6 is a map of steering torque and motor output torque.

FIG. 7 is a map of a vehicle speed, a vehicle speed coefficient, and a coefficient β.

FIG. 8 is a diagram illustrating a relationship between a conventional steering angle and a steering torque.

[Explanation of symbols]

 Reference Signs List 10 steering wheel 12 steering shaft 14 steering gear box 22 motor 24 electromagnetic clutch 26 steering angle sensor 28 torque sensor 32 electronic control unit 34 vehicle speed sensor 56 alarm lamp M1 calculation means M2 first correction means M3 control means M4 second correction ratio Reduction means M5 electric motor

Claims (1)

(57) [Claims] A calculating means for calculating an auxiliary steering force based on a steering torque; and a value decreasing as the vehicle speed increases as the vehicle speed increases.
First correction means for multiplying the auxiliary steering force by a smaller correction coefficient to reduce the auxiliary steering force, and performing drive control of an electric motor based on the corrected auxiliary steering force. In the electric power steering device that performs auxiliary steering by the electric motor, when the steering torque is equal to or more than a value corresponding to a saturation point of an output torque characteristic of the electric motor, a rate of decrease correction based on the vehicle speed of the first correction means. An electric power steering apparatus, comprising: a second correction unit that corrects the power reduction.